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Charged Coupled Device Imaging

Charged Coupled Device Imaging. By Marc Castro 17443948. CCD Imaging Process. (3 step process) 1. Exposure Converts light into an electronic charge at discrete sites called pixels, photo sites, photodiodes or capacitors. 2. Charge Transfer One of the CCD architectures is used.

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Charged Coupled Device Imaging

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  1. Charged Coupled DeviceImaging By Marc Castro 17443948

  2. CCD Imaging Process (3 step process) 1. Exposure Converts light into an electronic charge at discrete sites called pixels, photo sites, photodiodes or capacitors. 2. Charge Transfer One of the CCD architectures is used. 3. Charge to voltage Signal conversion from analog (electrical charges) to digital (0’s and 1’s).

  3. How does it look like? Charged Couple Device

  4. What is it? • Charged Coupled Device (CCD) • an analog shift register, that enables the transportation of analog signals (electric charges) through successive stages (pixels) controlled by a clock signal. • Primary uses: • Memory • Delaying samples of analog signals • In an array of photoelectric light sensors (image sensors)

  5. History • Invented in 1969 • Creators: Willard Boyle and George E. Smith • Location: AT&T Bell Labs. Currently part of Lucent Technologies • Motivation: the lab was working on the picture phone and on the development of the semiconductor bubble memory. • CCD – originally designed as an electronic memory device that can be charged by light.

  6. CCD Fabrication • Made using photolithography techniques. Individual pixel gate fabricated on a silicon wafer Courtesy of Olympus

  7. End Product Don Groom LBNL

  8. Capturing Images The CCD - comprised of many individual signal capture units (photo sites, capacitors, pixels) CDD - 2D Pixel Array

  9. Capturing Images How charges are stored • CCDs are comprised of pixels (capacitors) which are MOS (Metal Oxide Semiconductors). • MOS allow electron charges to build up within the wells.

  10. Capturing Images • Light – incoming photons falls onto the surface of a pixel. • (CDD - 2D array of pixel elements) • Result- generates free electrons in the silicon of the CCD due to the photoelectric effect, proportional to the number of photons striking it. These electrons collect in little packets. • Point- the total charge is proportional to the light intensity at that pixel. • A brighter image ( higher electrical charge). • A darker image ( lower electrical charge). • Drawback- only measures intensity. Not color!!! • CCD’s normally have 1 to 5 million packets of charge.

  11. CCD Scanning Formats CCDs can be used to collect an image in one of three ways, either one pixel at a time, one row at a time, or as an entire area at once.

  12. Methods to capture color Method 1: Beam Splitter Method 2: Bayer Pattern Courtesy of HowStuffWorks

  13. 2-D Pixel Array with Bayer Pattern • Used over the CCD (color grid over imaging array) • Each square (4 pixels) contains • One red • One blue • Two green

  14. Transfer image from array. • General Idea – • Control circuit causes each pixel to transfer its contents to its neighbor using a clocking scheme. The last pixel in the array dumps its charge into a charge amplifier, which converts the charge into a voltage. • The controlling circuit converts the entire semiconductor contents of the array to a sequence of voltages, which it samples, digitizes and stores in some form of memory.

  15. Readout Architecture • Full Frame • Frame Transfer • Interline • They are the most common

  16. Full Frame Architecture Courtesy of Molecular Expressions

  17. Frame Transfer Architecture Courtesy of Molecular Expressions

  18. Interline Architecture Courtesy of Molecular Expressions

  19. Storing the image • Analog to digital converter • Samples the analog signal and turns the information into bytes of (1’s and 0’s). • Charge amplifier – converts the charge into voltage. • Record bytes in a storage medium • Memory Cards • Hard Drive • DVD

  20. Applications Digital Photography Astronomy Sensors Electron Microscopy Medical Fluoroscopy Optical and UV Spectroscopy

  21. Devices • Astronomical Telescopes • Scanners • Bar code readers • Machine vision for robots. • Optical character recognition (OCR)

  22. Works Cited • Tom Harris. “How Camcorders Work.” HowStuffWorks.http://electronics.howstuffworks.com/camcorder.html • “Charge-coupled device.” Wikipedia. http://en.wikipedia.org/wiki/Charge-coupled_device • “Building A Charge-Coupled Device.” Olympus Microscopy Resource Center. http://www.olympusmicro.com/primer/java/photomicrography/ccd • Tom Thompson. “Charge-Coupled Device.” ComputerWorld. http://www.computerworld.com/softwaretopics/software/multimedia • “What is a Charge-Coupled Device.” Tech-Faq. http://www.tech-faq.com/charge-coupled-deivce.shtml • Lucent Technologies. “CCD-The History of CCDs or Charge Coupled Devices.” About.com Inventors. http://inventors.about.com/od/cstartinventions/a/CCD.html • “Charge-Coupled Device (CCD) sensor.” MIR. http://www/mir/com.my/rb/photography/digitalimaging/ccd/html • “Charge-coupled deivce.” Whatis.com. http://searchstorage.techtarget.com/sDefinition/0,,sid5_gci295633

  23. Works Cited • “Anatomy of a Charge-Coupled Device.” Molecular Expressions Optical Microscopy Primer: Digital Imaging in Optical Microscopy. http://micro.magnet.fsu.edu/primer/digitalimaging/concepts • Eric Meisenzahl. “Charge-Coupled Device Image Sensors.” Eastman Kodak Co. http://engage.advanstar.com/jnserver/acc_random • “Charge-couple device.” Answers.com. http://www.answers.com/topic/charge-coupled-device

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